MATERIALS AND MOLDING METHODS 



4-15 



Although relatively expensive, unicellular plastic foams, in addition to providing buoy- 

 ancy have the following important advantages to warrant their use as core materials: 



Lightweight. 



Resistance to water, fungi and decay. 



Can be foamed in place - polyurethane or expandable polystyrene beads (24,25). 



Are available in prefoamed logs, boards or rods and can be easily cut, shaped 

 and bonded - cellular cellulose acetate and polystyrene (26,27). Unlike the lower 

 cost prefoamed polystyrene, cellular cellulose acetate does not dissolve in resins. 

 Fig. 4-13 illustrates the use of foam plastics as a core material. 



Fig. 4-13. Polyurethane foamed in place 

 cores for main longitudinals of 36' LCVP 

 test section /"Courtesy Budd Company) 



Honeycomb 



Honeycomb cores of aluminum, fiber- 

 glass laminates, cotton duck and water- 

 proof paper are available in various sizes 

 and weights (27,28). Waterproof paper 

 honeycomb core sandwich construction, 

 Fig. 4-14, is the most commonly used 

 in boats for interior bulkheads, decks, 

 seats, etc. 



Fig. 4-14. Sandwich Panel with 

 Waterproof Paper Honeycomb Core 



